Essentially all of the primary mercaptans are made commercially in the United States by the ultraviolet light promoted addition of H.sub.2 S to 1-olefins. A typical batch reactor for a mercaptan includes a large vessel containing an appropriate number of long cylindrical mercury vapor lamps, each of which is surrounded by a tubular quartz well that is immersed in the reaction solution. The contents of the reactor are energetically stirred, and the reaction can be batch or continuously operated. Commercial operation of such reactors, however, results in a large amount of heat produced by the ultraviolet lamps, which is mostly removed by water flowing in a jacket surrounding the reactor.
In reactors of this kind the intensity of the ultraviolet light reaching the reaction mass is often reduced by discoloration of the quartz well due to soot buildup on its outer surface. Accordingly, the efficiency of the lamp is greatly diminished by prolonged use. After a relatively short period of time the reactor is no longer efficient for producing the desired product, and eventually the reaction rate retards to a point where the reactor must be shut down so that maintenance crews can enter the reactor and manually clean the lamp wells.
Attempts to keep the lamp wells clean by circulating cleaning solution in the reactor have met with little success. A large number of cleaning fluids have been suggested for circulating in the reactor to continuously clean the lamp wells. Trial solutions consisted of: hydrocarbons including: pentane, o-xylene, isooctane, and hydrofluoric heavy alkylate; ketones including: acetone, and methyl isobutyl ketone; other compounds including: methyl tertiary-butyl ether, t-butyl disulfide, 1,1,1-trichloroethane, n-methyl pyrrolidone, ethylene glycol and glycerin; aqueous solutions including: 5% NaOH, 5% Na.sub.2 S.sub.2 O.sub.3, 5% Na.sub.2 CO.sub.3, and 2% NaOH; mixtures including: toluene/sulfolane, 30% H.sub.2 O.sub.2 and detergent, and Na.sub.2 PO.sub.4 and detergent; other solutions including: Dextron II transmission fluid, and type F transmission fluid. It is further known that other types of cleaning systems for UV lamp wells, which are not thought to be useful in photochemical reactors, have been proposed. For example, automatically controlled scraping devices may be employed to scrape deposits off of the UV lamp wells employed in water purification systems.
Accordingly, a long felt need remains for an effective method for continuously cleaning of the UV lamp wells in the photochemical reactor using mercury vapor or other UV light producing lamps for promoting a chemical reaction.
It is an object of this invention to increase production from a photochemical reactor by sustaining the initial reaction rate for a longer period of time.
It is another object of this invention to decrease downtime maintenance required in operating a photochemical reactor.
It is a more specific object of this invention to provide a self cleaning system which continuously clean lamp wells while the reactor is operating so as to maintain a high efficiency for the photochemical reaction.
It is another object to provide a cleaning system for UV reactor lamp wells which is both durable and economical of construction.
Still another object is to allow the operator of the reactor to schedule downtime for maintenance without considering unpredictable fouling time of the ultraviolet lamp wells.